Serialization and Deserialization Bullet points from Head First Java, Ch. 14

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Serialization and DeserializationBullet points
from Head First Java, Ch. 14
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saving an object between program runs

• you can save an objects state by serializing the
  object
• to serialize an object, you need an
  ObjectOutputStream (from the java.io package)
• streams are either connection or chain streams
• connection streams can represent a connection to
  a source or destination
• typically a file, network socket connection, or
  the console
• chain streams cannot connect to a source or
  destination
• they must be chained to a connection (or other)
  stream
• to serialize an object to a file, make a
  FileOutputStream and chain it into an
  ObjectOutputStream
• to serialize an object, call writeOjbect(theObject
  ) on the ObjectOutputStream
• you do not need to call any methods on the
  FileOutputStream

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Serializable interface

• by default, objects are not serializable
• to be serialized, an object must implement the
  Serializable interface
• Serializable is an empty interface
• it has no methods that must be implemented
• its presence is a signal to the runtime that this
  object can be serialized
• if a superclass of the class implements
  Serializable, the subclass can also be serialized
• even without explicitly declaring implements
  Serializable

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the object graph

• when an object is serialized, its entire object
  graph is serialized
• including any objects referenced by the
  serialized objects instance variables
• plus any objects those objects reference, and so
  on
• if any object in the graph is not serializable,
  an exception will be thrown at runtime
• unless the instance variable referring to the
  un-serializable object is skipped
• the transient keyword can be used to do mark an
  instance variable to be skipped
• an instance variable marked as transient will be
  restored as null upon deserialization
• or the default value for a primitive

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deserialization

• using readObject(), read objects in the order in
  which they were originally written
• the return type of readObject() is Object
• deserialized objects must be cast to their
  original type
• static variables are not serializable
• it doesnt make sense to make static variables
  part of a particular objects state, since all
  objects of that type (made from that class) share
  only a single static value

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